Yasushi Shigeri (1,#), Shunji Shinohara (2), Shunji Murata (2), Masafumi Fujimoto (1) and Kazuo Kawasaki (2)
(1) Shionogi Research Laboratories, Shionogi and Co., Ltd., 5-12-4 Sagisu, Fukushima-ku, Osaka 553, Japan (2) Discovery Research Laboratories II, Shionogi and Co., Ltd., 3-1-1 Futabacho, Toyonaka, Osaka 561, Japan (#) Present address: Department of Organic Materials, Osaka National Research Institute, Agency of Industrial Science and Technology, Ministry of International Trade and Industry, 1-8-31 Midorigaoka, Ikeda, Osaka 563, Japan
Abstract: Electrophysiological responses to cholecystokinin (CCK) were studied in Xenopus oocytes injected with mRNA from rabbit pancreas or rat hippocampus. CCK-octapeptide(26 - 33) (sulfated form) (CCK-8) elicited inward currents in both groups. In oocytes injected with pancreatic mRNA, CCK-8-induced currents were composed of two components, fast and slow. However, in oocytes injected with hippocampal mRNA, fast currents disappeared. The potency ranking of the agonists and the antagonist indicated that the receptors expressed by pancreatic and hippocampal mRNA were CCKA- and CCKB-subtypes, respectively. Extracellular application of EGTA had little effect on the CCKB-mediated response, but attenuated the CCKA-mediated one. Intracellular injection of EGTA abolished the CCKB-mediated response, whereas small smooth currents remained in oocytes expressing the CCKA-receptor. The reversal potentials of the CCKA- and CCKB-receptor-mediated responses were consistent with that for Cl- currents. However, the reversal potential of the small smooth currents in EGTA-loaded oocytes expressing the CCKA-receptors was close to that for a non-selective cation channel. These results suggest that CCK-8 activates at least two different channels, a Ca2+-dependent Cl- channel and a non-selective cation channel in oocytes expressing the CCKA-receptor, while the CCKB-receptor elicits only a Ca2+-dependent Cl- channel.
Keywords:
Cholecystokinin (CCK), Xenopus oocyte, Electrophysiology, CCKA-receptor, CCKB-receptor